A conventional hinge mechanism used for a vehicle-mounted monitor apparatus will be discussed with reference to FIG. 6 and FIG. 7. FIG. 6 is a perspective view showing an arrangement of a conventional hinge mechanism 21 having a click action, and FIG. 7 is an exploded perspective view thereof. The hinge mechanism 21 is arranged such that a rotation shaft 3 connected to a monitor 13 and rotating about a rotating central axis X is fit in a resilient member 6, a base 2, a leaf spring 4, and a plate 5 to be caulked.
The rotation shaft 3 is provided with a flange 3a having a radius larger than that of a rotation shaft hole 2a of the base 2, and a D-cut section 3b having a radius smaller than that of the rotation shaft hole 2a and having a pair of flat faces formed symmetrically. On the other hand, the rotation shaft hole 2a to be rotatably inserted into by the D-cut section 3b of the rotation shaft 3 is formed in the base 2. Further, insertion holes 4a, 5a, and 6a are prepared in the leaf spring 4, the plate 5, and the resilient member 6, respectively, and are fitted in the D-cut section 3b of the rotation shaft 3. The insertion holes 4a, 5a, and 6a each have an area larger than the sectional area of the D-cut section 3b by the dimension of a fit.
Further, a plurality of click recesses 2b1, 2b2 is concavely provided in the base 2 at a predetermined interval on a circumference centering the rotating central axis X, and also a housing position determining recess 2c is concavely provided in an angular position where the monitor 13 is housed in a monitor main body. A tapered face 2d is formed by gradually reducing the depth of the housing position determining recess 2c from the housing position determining recess 2c toward the click recess 2b1. On the other hand, a click projection 4b that fits in the click recesses 2b1, 2b2 and the housing position determining recess 2c of the base 2 to thus produce a click action is provided in the leaf spring 4.
FIG. 8A to FIG. 8C are views showing the opening and closing operation of a ceiling-mounted monitor apparatus 11 including the hinge mechanism 21 as shown in FIG. 6 and FIG. 7. FIG. 8A is a perspective view showing a state where the monitor 13 is housed in a monitor housing case 12, and FIG. 8B is a schematic sectional view thereof. FIG. 8C is a perspective view showing a state where the monitor 13 is opened. The ceiling-mounted monitor apparatus 11 consists of the monitor housing case 12 located on the side of the main body mounted on a ceiling of a vehicle, and the monitor 13 that can be folded and unfolded by the opening and closing with respect to the monitor housing case 12. A monitor screen 13a is provided on one face of the monitor 13. Further, the monitor 13 is locked by a lock 15 associated with a button 14 to be held within the monitor housing case 12. At that time, the hinge mechanism 21 is placed in a condition such that the click projection 4b of the leaf spring 4 is fitted in the housing position determining recess 2c of the base 2. The rotation shaft 3 is rotated integrally with the leaf spring 4, the plate 5, and the resilient member 6 about the rotating central axis X with respect to the base 2 installed on the side of the main body of the monitor apparatus, and thereby the monitor 13 connected to the rotation shaft 3 is also rotated (folded and unfolded) about the rotating central axis X.
As the button 14 provided on the monitor housing case 12 is pushed, the lock 15 holding the monitor 13 is released as shown by a dash-single-dot line in FIG. 8B, and the monitor 13 is rotated by self-weight to an angle of a self-weight fallen position (to a position of the monitor 13 depicted by the dash-single-dot line in FIG. 8B) about the rotating central axis X. At that time, in the hinge mechanism 21, the click projection 4b of the leaf spring 4 slips out from the housing position determining recess 2c of the base 2, and slides on the tapered face 2d due to the self-weight of the monitor 13. Thereafter, a user moves manually the monitor 13 to the viewing position shown in FIG. 8C to enjoy the image. At that time, in the hinge mechanism 21, the click projection 4b fits in the click recess 2b1 or the click recess 2b2 to thereby hold the monitor 13 at the angle of the viewing position.
Moreover, a rotary mounting mechanism disclosed in Patent Document 1 is also arranged to have a click action as in the hinge mechanism 21 discussed above, and includes a base member provided with an insertion hole; a rotation shaft which is inserted into the insertion hole of the base member and rotatably attached thereto about the axis thereof; a click plate having a recess for a click function provided in the face thereof opposing one face of the base member; and a click spring, which has resiliency in the direction parallel to the axis of the rotation shaft, has formed therein a protrusion for a click function, which fits in the recess of the click plate, is non-rotatably fixed to the base member, and also is resiliently attached between the base member and the click plate such that the base member, the rotation shaft, and the click plate are pressed into contact with each other in the direction parallel to the axis of the rotation shaft. Therefore, when the rotation shaft is rotated with respect to the base member, the protrusion for a click function fits in and slips from the recess, to thereby produce a click action.
Furthermore, a hinge mechanism disclosed in Patent Document 2 is arranged as follows: a plurality of friction members are pressed into contact with a rotation member by a resilient member; when the rotation member is rotated, friction is caused between the rotation member and the friction members; thus, the rotation member can be rotated only when rotation torque larger than a predetermined rotation one is applied thereon. In the case of the arrangement, the following torque (hereinafter, referred to as “holding torque”) is provided: at any angle of the rotating body connected to the rotation member, the rotating body cannot be rotated unless applied thereon with any of the same predetermined torque or larger, and therefore the rotating body can be held at any angular position.